In the course of these studies of interacting influences of metabolically active and inert respiratory gases, it was discovered that incapacitating itching, formation of dermal lesions and severe vestibular functional derangement developed in man surrounded by helium at elevated ambient pressure while breathing a heavier inert gas such as nitrogen or neon. Subcutaneous gas bubble formation with dermal lesions were produced in animals subsequently under similar circumstances (i.e., breathing argon, nitrogen or neon while surrounded by helium at increased pressure). Through administration of nitrous oxide to animals surrounded by helium at atmospheric pressure, it was learned that the extensive cutaneous gas lesions develop without a change in pressure and further that massive and continuous gas embolization of the lungs results from the formation of bubbles in subcutaneous capillaries throughout the body. These gas lesions and continuous gas embolization at fixed ambient pressure represent a new biophysical and pathological phenomenon potentially to be encountered in unusual environmental and medical circumstances whenever the pattern of exposure to ambient and respiratory inert gases differs appropriately in solubility and diffusivity. The phenomenon is termed "Isobaric Gas Counterdiffusion Syndrome." The present extension of the overall study of respiratory gases involves further investigation of the biophysical mechanisms, study of the dynamics of gas exchange between ambient atmosphere and cutaneous vascular bed, quantitative study of rates of development of gas lesions and gas embolization over a large range of ambient pressures, investigation of gas lesion development in the eye, and study of influences of isobaric gas counterdiffusion upon auditory and vestibular function.